This invention relates to gas turbine combustors generally, and more specifically, to a novel endcover assembly for the forward or upstream end of a gas turbine combustor.
In certain gas turbines, a plurality of combustors are arranged in an annular array about the turbine rotor to provide for the combustion of fuel and guide the energized combustion products into the turbine section to drive the turbine. Each combustor typically includes an outer casing which defines the external boundary of the combustor; a flow sleeve for distributing compressor discharge air to the head end of the combustor while also cooling a liner which encloses the combustion chamber; and a transition piece for flowing the combustion products into the turbine section. The combustor also includes a plurality of fuel nozzles coupled to an endcover. Air and fuel is supplied through the endcover to the fuel nozzles for combustion within the liner. The endcover thus functions to close the combustor forward end, to support the fuel nozzles, and to distribute air and fuel to the fuel nozzles.
Endcover designs for turbine combustor systems typically have included a plate mounting each fuel nozzle individually. In prior endcover assemblies of this type, the internal passages for the air and fuel were located in the fuel nozzle, separate and apart from the endcover. A follow-on generation of endcovers provided air and fuel passages internal to the endcover. This was done to accommodate a plurality of nozzles for each endcover rather than one fuel nozzle per endcover as in prior conventional combustors. While that change simplified the fuel nozzles and enabled the mounting of a plurality of fuel nozzles onto the endcover, the complexity of the endcover was increased in order to provide the integrated air and fuel manifolds and necessary multiple passages for the fuel nozzles carried thereby. Extra parts were necessary, such as inserts, to render complex passages in the endcovers possible. Brazed joints were also included to seal these extra parts, including inserts in the endcovers. A further generation of endcovers for turbine combustors followed. These endcovers employed even more complicated brazed joints between the endcovers and their various parts. However, cracking of the brazed joints was observed on these more recent endcovers.
In addition, certain turbine model endcover assemblies formed with internal passages as noted above also require premix gas flow orifices (also referred to herein as “flow restrictors”, or “flow restrictor inserts”) pressed and staked into place on the “hot side” of the combustor endcover plate (that side exposed to combustion in the combustion chamber). The location of the flow restrictor within the passageway in the endcover defines the acoustic length from the fuel nozzle gas exit holes at the cold-side of the endcover to the orifice restriction proximate the hot side of the endcover. The acoustic length has a natural frequency that can be negatively impacted by combustor dynamics which vary with site conditions and fuel variation. Accordingly, there is a need to provide endcovers with orifice restrictors that can accommodate acoustic length adjustments (preferably on site), favorable to combustor dynamics.